GREENFIELD — If you live in the Greenfield area, odds are you have been called to the window or porch in July by the blast furnace sound of gas burners, and stayed to watch the bright procession of hot air balloons drifting overhead.

Imagine standing at the top of Poet’s Seat Tower with the roar of a flame above your head, the ground swaying gently beneath your feet and the landscape drifting serenely below.

While the music has very nearly stolen the stage, the Green River Festival began as and remains a hot air balloon festival, now, in fact, the only one in western Massachusetts.

The Greenfield Chamber of Commerce’s annual festival returns this weekend and hot air balloons are as always a major facet, weather permitting.

Tuesday’s promotional flight began shortly after 6 in the morning because this week’s extreme heat makes flying “lighter than air” craft very difficult in the late afternoon.

A blast from the propane burner heats the partially inflated polyester balloon and quickly jerks the basket upright. Everyone clambers in, a further blast and the basket lifts almost imperceptibly from the Greenfield Community College parking lot.

In the basket the burner is loud enough to drown out conversation and the passenger can look down on the backyards, up into the flame and the carnival-tent belly of the balloon, or out across the county to the horizon in every direction.

From above, at heights ranging from eye-level with the treetops to 1,500 feet, the county looks very different. Familiar landmarks like the Franklin County Fairgrounds and cemeteries are transformed by perspective; the cemeteries seem less populated and the horse track covers more of the fairgrounds than it seems from the ground.

Paul Sena steers his balloon by heating and releasing the air in the balloon, rising and falling between the strata of diverging air currents — earlier charted through online reports and confirmed through the release of a helium balloon — but stays within easy sight of the ground.

Unlike the vast, perfectly serene landscapes visible to airplane passengers lucky enough to get a window seat, the view from the balloon is alive with detail.

A small group is braving the recently unpredictable water levels to camp on a small island in the Deerfield River. Five dogs enjoy a walk on a dirt road along the edge of a field. The Astilbe flowering in long rows in another field are easily identifiable.

“You get really high up, it feels like you’re standing still while the whole world spins below you,” Sena said, explaining his preference for the lower air.

Below, tractors move through a field and a small flock of birds swirls and settles around the intersection of two dirt roads.

“We’re so lucky to live here,” comments Lesley Kayan of Northfield, one of three passengers this morning. The balloon has just passed by the transfer station and over the fairgrounds and the rotary is next in view, but the landscape is overwhelmingly green and wooded despite these familiar patches.

Kayan’s husband, Joe, is the ground crew. He follows the balloon from below in Sena’s truck and eventually collects the balloon, pilot and three passengers from a fallow field off Old Mill Village Road in Deerfield.

Sena announced early in the flight that he was shooting for a landing south of Old Deerfield, and delivered.

Hot air balloons operate on relative air density, manipulated via temperature: if the air outside the balloon is too hot the burner will have to work harder and the fuel supply won’t last as long. Additionally, Sena points out, adding the heat of the burner immediately above the heads of the passengers to a 90 degree day is not comfortable.

It’s been a bad year for ballooning. Sena said he has had to cancel 60 percent of his scheduled flights, mostly due to rain. Rain steaming off the surface of the balloon will damage the envelope, he said.

Lately, the evenings have been too hot, but conditions for the morning flight are perfect.

Maneuverability is weather dependent, and Sena says the morning’s air currents give him a 90 degree steerage. The term calls to mind ships, as does the balloon; the sail-like envelope is rigged to the basket with nautical rope and shackles.

Sena sees the balloon as swimming the air.

“They call us bottom divers in a sea of air,” he said.

As the only full-time professional hot air balloon pilot in western Mass., he owns and operates Worthington Ballooning. Sena spends half his time west of the Berkshires and half east.

He has flown movie stars, moguls, carried small weddings, sees two or three engagements per year and recalls only one proposal that fizzled. He remembers the remainder of the ride as quiet.

Usually, he flies two couples at a time, but balloon rides aren’t exclusively a romantic activity.

“Singles, friends, a lot of people have it on their bucket list, want to take a balloon flight,” he said. “It’s such a peaceful thing to do.”

Sena is the Green River Festival’s “balloon-meister,” directing this year’s complement of 11 balloons. He began attending the festival in the early 1990s and has organized the balloon portion of the festivities, including rides, short tethered flights and the tricky-to-coordinate illumination, for 12 years.

The Franklin County Chamber of Commerce runs the event, which from its 1986 origins as the balloon festival has grown to a full weekend of music on three stages, by local and national acts, with balloons framing the festival and providing a floating reminder of the event.